In the long term, feeling full is about calories. In the short term, the body takes a major cue from the amount of fat in a meal, particularly saturated fat, which of course you're getting neither of. Try switching to regular yogurt and see if that helps.

You can make "Greek" yogurt from your current yogurt by suspending it in a muslin or cheesecloth and letting it drain (I line a colander with an old, clean pillowcase and put the yogurt in there, with the entire thing over a bowl to catch drips). A bunch of whey will drain out, and if I remember correctly, it will take a lot of milk sugars with it, leaving you with a yogurt that has a higher protein concentration than before.

If you are trying to stay satisfied, I recommend what I've been eating for breakfast: four ounces full fat, plain yogurt, a variety of 10 to 15 unsalted nuts (currently Brazil, almomds, hazelnuts, walnuts, macademia, and pine nuts for me), a mixture of pumpkin, sunflower, flax, sesame, and hemp seeds, a few chips of unsweetened coconut, four sliced strawberries, raspberries, blackberries, blueberries, cherries, and an apricot, topped with no more than 1 teaspoon honey. Along with that I drink one cup of coffee to which I add one cup of hot milk, which I foam. I eat around 6:30 and just vaguely begin to get hungry about noon or 1 pm. For years, I had always eaten a good breakfast, but would be starving by 10:30 No more!

PS You might as well be drinking a glass of non fat milk with sugar in it--that is what vanilla yogurt is, with a few additional bacteria. The sugar is making your blood sugar spike and then drop. Good fats are not your enemy, so add some to your diet and I'll bet you'll notice a big difference. I am highly skeptical of this low fat obsession--I lost weight when I ditched the low fat milk and yogurt in place of the full fat milk.